Fiber optic networks have the potential for greatly increasing telecommunication bandwidths and data rates. The demand for increased capacity continues to grow, especially as more and more information is transmitted across the Internet.
One limitation of fiber optic networks as currently implemented is their inability to directly switch from a fiber on a source network or network node to a fiber on a destination network or network node. Instead, optically encoded data are dropped from the source network fiber, converted to electrically encoded data, switched to the destination network using conventional electronic switches, converted back into optically encoded data, and injected into the destination network fiber.
Micromachined mirror arrays offer the ability to directly switch optically encoded data in devices, known as all-optical cross connect switches, from a source fiber on a source network to a destination fiber on a destination network without having to convert the data from optical to electronic and back again. For such mirror arrays to be commercially useful, they must be able to cross connect approximately 1000 input fibers with an equal number of output fibers in a compact volume. This can be achieved with mirrors that can be densely packed together and that are rotatable by relatively large angles in an arbitrary angular direction.
Recent developments in the field of microelectomechanical systems (MEMS) allow for the bulk production of microelectromechanical mirrors and mirror arrays that can be used in all-optical cross connect switches. MEMS-based mirrors and mirror arrays can be inexpensively designed and produced using conventional tools developed for the design and production of integrated circuits (IC's). Such tools include computer-aided design (CAD), photolithography, bulk and surface micromachining, wet and dry isotropic and anisotropic etching, and batch processing. In addition, deep reactive ion etching methods (DRIE) allow silicon devices to be produced having high aspect ratios (˜20:1) that rival those that can be achieved using the prohibitively expensive lithography, electroplating and molding process (LIGA) which requires access to a synchrotron radiation source. (LIGA is an acronym for the German lithographic, galvanoformung und abformung).
A number of microelectromechanical mirror arrays have already been built using MEMS production processes and techniques.
A dual-axis design was developed by Analog Devices (De Gaspari, J., “MEM's Rocky Road,” Mechanical Engineering, June, 2002, p.38.). In this device, the mirror is suspended by a first set of opposing springs in a rotatable frame. The rotatable frame is suspended by second set of opposing springs that allow rotation in an orthogonal direction. Although this approach allows for dual axis rotation, the method of actuation is unclear and the frame requires additional space that limits how closely packed the mirrors can be arranged.
In U.S. Pat. No. 6,283,601, Hagelin et al disclose a mirror system in which the mirror is fixed to a post mounted on a support plate. The support plate is rotated by connectors that tilt the edge of the support plate in response to actuator displacements. An issue not addressed in Hagelin et al is the desire to rotate the mirror without displacement.
In U.S. patent application Ser. No. 09/779189 of Nasiri, filed on Feb. 7, 2001, and hereby incorporated by reference in its entirety, a mirror is mounted on a support post mounted on a freely moving plate. In Nasiri, two orthogonally oriented pairs of rotatable actuators are coupled to the freely moving plate by gimbal springs. By properly coordinating each pair of actuators, the plate center can be rotated without displacement under ideal conditions.
Although the Nasiri application shows improved ability to manipulate the plate center without displacement, the performance of similar configurations can be greatly improved by paying special attention to the system used for transmitting rotation from the actuators to the freely moving plate.